High voltage electron discharge tube having an anode target

ABSTRACT

In high voltage electron tubes, such as type RCA 6BK4, comprising a cathode, and an open-ended tubular anode including an electron receiving target within the anode tubulation, the target is made from a refractory metal such as molybdenum or tantalum, coated with chromium.

United States Patent Patented Janet L. Deckert Red Bank, NJ. 811,724

Apr. 1. 1969 June 29, 1971 RCA Corporation inventor Appl. No. Filed Assignee HIGH VOLTAGE ELECTRON DISCHARGE TUBE HAVING AN ANODE TARGET 4 Claims, 1 Drawing Fig.

U.S.C1 n 313/311, 313/331, 313/313, 29/25.14 Int. Cl 1-101j l/05, HOlj 1/14 Field ofSearch 313/311,

[56] References Cited UNITED STATES PATENTS 3.444.417 5/1969 Stephensv 1 Y 313/331 3,456,147 7/1969 Stephens 313/331 X FOREIGN PATENTS 138,575 10/1947 Australia. 313/311 1,014,907 12/1965 Great Britain 313/313 Primary Examiner-James D. Kallam Assistant Examiner-Andrew J 1 James Attorney-G. H. Bruestle ABSTRACT: In high voltage electron tubes, such as type RCA 6BK4, comprising a cathode, and an open-ended tubular anode including an electron receiving target within the anode tubulation, the target is made from a refractory metal such as mo1ybdenum or tantalum, coated with chromium.

HIGH VOLTAGE ELECTRON DISCHARGE TUBE HAVING AN ANODE TARGET BACKGROUND OF THE INVENTION This invention relates to electron discharge devices, and particularly to high voltage regulator tubes.

High voltage regulator tubes, such as type RCA 6BK4, are used, among other places, in the high voltage power supplies of color television receivers. In such applications, the voltage on the anode ofthe tubes can reach as high as 34,000 volts.

A problem associated with the use of such tubes at these high anode voltages is that electrons passing from the tube cathode to the tube anode are accelerated to such a high velocity that X-radiations are produced at the anode. To prevent escape of the X-radiations, elaborate shielding means are used.

The RCA 6BK4 tube, for example, comprises an elongated, open-ended tubular anode containing a disclike molybdenum target within the anode tubulation about midway of the tubulation length. Electrons from the cathode pass into the anode through the open end thereof and are collected by the target. X-radiations produced at the target are mostly shielded by the sides of the tubular anode, although some X-radiations escape through the open end of the anode.

In some instances, it is desired to even further reduce the amount of X-radiations escaping from the electron tube. Proposals of means for further reducing the escape of X-radiations comprise the use of extra metal members within the anode in surrounding relation with the target, and-the use of extra thick tube envelopes. These proposed means, however, add undesired expense to the tube.

SUMMARY OF THE INVENTION In high voltage electron tubes comprising a source of electrons, and a tubular anode containing an electron receiving target within the anode tubulation, the target is made from a plate of refractory metal, such as molybdenum or tantalum, the plate being clad with chromium.

DESCRIPTION OF THE DRAWING The drawing is a side view, partly broken away, of an electron tube made in accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The illustrative tube 2 shown in the drawing is a standard RCA 6BK4 voltage regulator with the exception of the anode target.

The tube 2 comprises a glass envelope 4 and a base 6. Terminals 8 extend through the base 6 and into electrical contact with a cathode l and a grid electrode 11 (only the lateral wire winding thereof being visible) disposed within a shield member 12. The shield member 12 has an opening 14 through the upper surface 16 thereof, allowing egress of a beam of electrons from the cathode during operation of the tube.

Disposed in longitudinally spaced relation with the shield 12 is an elongated three-part tubular anode electrode 20 comprising two cylinders 22 and 24, and a terminal member 26. The lower cylinder 22 has an open end 28, and has, at the other end thereof, an annular flange 32. The upper cylinder 24 has, at its lower end, an annular flange 36. Disposed between the two cylinders 22 and 24, and transverse to the longitudinal axes thereof, is an electron target 40. The target 40 is clamped between the two flanges 32 and 36 of the two cylinders 22 and 24 respectively, and the two cylinders are secured together by means of the flange 32 of the cylinder 22 being clamped around the flange 36 of the upper cylinder 24.

The upper end 44 of the cylinder 24 is secured, as by welding, to the terminal member 26, which extends outwardly through, in sealed relation with, the upper end of the glass envelope 4.

The anode cylinders 22 and 2 4 are made, in the illustrative embodiment, of aluminum clad steel. The target 40 comprises a plate of a refractory metal, such as molybdenum or tantalum, having a thickness in the order of IO mils. The target plate is clad or coated with a thin layer of chromium. The chromium cladding need coat only the electron receiving side of the target, although, as a practical matter, the usual cladding processes result in all surfaces of the target being coated.

In a preferred embodiment, the target coating comprises a flash of chromium, i.e., a layer of chromium having a thickness in the order of 0.1 mil.

In operation of the tube 2, a beam of electrons is emitted through the opening 14 in the shield member 12 and enters the anode 20 through the open end 28 of the cylinder 22. The electron beam impinges upon a small circular area of the target, the diameter of the area being, it is estimated, in the order of0.060 inch. 7 I 7 With an anode voltage in the order of about 30,000 volts, and an electron beam current of about 1.5 mils, the target is thus subjected to a high velocity electron beam conveying about 45 watts of power. It is estimated that the target in the standard 6BK4 electron tube, containing a molybdenum target 40 of 5 mils thickness, is heated to a temperature in the order of l300 C., with portions, or hot spots, reaching temperatures in the order of l500'C.

Tests have revealed that few metals are capable of withstanding the severe electron bombardment received by targets of the type described, i.e., comprising relatively thin plates not cooled by forced circulation cooling means. Targets made of steel and nickel, for example, were, in tests, quickly burned through by the electron beam. Tungsten, although not readily available in plate form, would otherwise probably be a suitable target material. About the only metals, readily available and not inordinately expensive, suitable for use as a target in such tubes, are molybdenum and tantalum. Molybdenum is a refractory material, having a melting point of about 2610 C., and has a relatively high thermal conductivity. Tantalum, while having a thermal conductivity considerably lower than that of molybdenum, has a higher melting point of 3300 C.

Chromium has a melting point considerably lower than that of tantalum, and a thermal conductivity considerably lower than that of molybdenum, hence is quite unsuitable for use as a target. Thus, the discovery that chromium can be used as a cladding on the target of such tubes, without causing vaporization of the metal cladding or degradation of the target for its intended use is an unobvious choice which provides unexpected results.

The chromium cladding, having a lower atomic number than the refractory base metal of the target, reduces the amount of X-radiations produced during operation of the tube.

Using a chromium plated molybdenum target 40, for example, the amount of X-radiations produced by a 6BK4 electron tube, in comparison with standard 6BK4 electron tubes using uncoated molybdenum targets, is reduced by 40 percent. In the comparison tests the tubes were operated with an anode voltage of 27,000 volts, and an anode current of 1.5 mils.

What I claim is:

1. A high voltage electron discharge tube comprising:

an electron source,

a tubular anode in spaced relation with said electron source;

and

an electron-receiving target within said tubular anode, said target comprising a chromium clad plate of molybdenum, tantalum, or tungsten.

2. An electron discharge tube as in claim I wherein said target has a thickness in the order of 10 mils, and said cladding of chromium has a thickness in the order of0.l mil.

3. An electron discharge tube as in claim I wherein said target comprises molybdenum.

4. An electron discharge tube as in claim 3 wherein said target has a thickness in the order of 10 mils, and said cladding of chromium has a thickness in the order of 0.] mil. 

1. A high voltage electron discharge tube comprising: an electron source, a tubular anode in spaced relation with said electron source; and an electron-Receiving target within said tubular anode, said target comprising a chromium clad plate of molybdenum, tantalum, or tungsten.
 2. An electron discharge tube as in claim 1 wherein said target has a thickness in the order of 10 mils, and said cladding of chromium has a thickness in the order of 0.1 mil.
 3. An electron discharge tube as in claim 1 wherein said target comprises molybdenum.
 4. An electron discharge tube as in claim 3 wherein said target has a thickness in the order of 10 mils, and said cladding of chromium has a thickness in the order of 0.1 mil. 